This invention pertains to both a novel and useful delivery device for administering a beneficial agent to produce a local or systemic physiological or pharmacological beneficial effect. The invention resulted from a chronic need for an agent delivery device, particularly gastrointestinal devices, that is easy to use, comfortable to the host, inexpensive and concomitantly can administer an agent at a continuous and controlled rate for a prolonged period of time at a desired functional rate, for example a drug dosage rate. This need existed in the medical, veterinary and pharmaceutical arts because prior attempts to achieve a prolonged release of a useful agent generally has led to unacceptable results. For example, many prolonged release preparations orally administered to achieve a prolonged result used assorted coatings designed to allow the release of the active agent after a certain time in the environment of use, such as in the gastrointestinal tract, led to problems that gave unacceptable results. One problem typically encountered in the gastrointestinal tract, is that in some cases soluble agent diffused through the coatings which often were insoluble in gastric fluids and in other cases some of the coatings resisted disintegration so that prolonged release preparations would pass through the gastrointestinal tract intact. Also, many agent coatings prepared in the past depended on the assumption that the stomach contents were very acid and the intestinal contents were basic to achieve disintegration of these coatings without any real consideration of the physiological variation of pH that can occur for these contents. Therefore, coatings which depended on pH for disintegration were not as efficient as planned and complete drug release was not obtained.
Other prolonged release medication involved the administration of coated particles or pellets, hard capsules and the like to produce a desired concentration of the agent in the environment of use such as the blood, but these two have not led to the desired agent levels. For example, if the dose of the agent gives a repeated administration effect, the concentration in the blood rises to peaks and falls to valleys depending on the number, frequency and availability of the doses. The peak-valley effect may not be satisfactory in terms of providing the best therapy, becuase at the peak, the high concentration may cuase side effects, and in the valley, the concentration may be insufficient to elicit suitable response. Thus, these types of prolonged release preparations, as with other alleged prolonged release preparations, often are not suitable for releasing agent at a controlled rate for a prolonged period of time.